The central character, Auguste Dupin, is idiosyncratic, more than a little egocentric, and somewhat of a recluse. He is highly observant and an expert at creating chains of reasoning based on his observations. His companion is a somewhat plain man in comparison to Dupin and primarily exists to serve as Dupin's foil, as well as functioning as an auditor for Dupin's explanations and a transmitter of his thoughts.
Had the routine of our life at this place been known to the world, we should have been regarded as madmen...
The heart of the story, as it is to become the heart of practically every detective story since, centers not on the action of the crime but rather on Dupin's explanation of how he solved it. The points about the murders which stump the police—the contradictory reports of neighbors as to the language they heard spoken and the fact that there seems no possible means of entering the room where the murders took place—are precisely those clues that enable Dupin to master the case. The first problem he accounts for by deducing that he criminal must have been an animal; the second he explains by following a mode of reasoning based on a process of elimination to determine that apparent impossibilities are in reality possible after all. When Dupin reveals that an escaped Ourang-Outang did the killing, he is content to have beaten the police at their own game; descendants of Dupin have been beating police inspectors ever since.
(The entire section is 250 words.)